The use of membranes to separate aromatics from saturates has long been pursued by the scientific and industrial community and is the subject of numerous patents.
U.S. Pat. No. 3,370,102 describes a general process for separating a feed into a permeate stream and a retentate stream and utilizes a sweep liquid to remove the permeate from the face of the membrane to thereby maintain the concentration gradient driving force. The process can be used to separate a wide variety of mixtures including various petroleum fractions, naphthas, oils, hydrocarbon mixtures. Expressly recited is the separation of aromatics from kerosene.
U.S. Pat. No. 2,958,656 teaches the separation of hydrocarbons by type, i.e. aromatic, unsaturated, saturated, by permeating a portion of the mixture through a non-porous cellulose ether membrane and removing permeate from the permeate side of the membrane using a sweep gas or liquid. Feeds include hydrocarbon mixtures, naphtha (including virgin naphtha, naphtha from thermal or catalytic cracking, etc.).
U.S. Pat. No. 2,930,754 teaches a method for separating hydrocarbons e.g. aromatic and/or olefins from gasoline boiling range mixtures, by the selective permeation of the aromatic through certain cellulose ester non-porous membranes. The permeated hydrocarbons are continuously removed from the permeate zone using a sweep gas or liquid.
U.S. Pat. No. 4,115,465 teaches the use of polyurethane membranes to selectively separate aromatics from saturates via pervaporation.
Japanese application 38478/65 describes an imide bond containing polyurethane elastomer prepared by casting an isocyanate with a tetracarboxylic acid dianhydride or acid anhydride by chain propagation of a prepolymer having terminal isocyanate groups derived from the treatment of a polyglycol with an organic di-isocyanate The polymer, made in a solution, can be spun or made into transparent yellow films.
Japanese application 19134/65 teaches the preparation of polyimide urethane copolymers by the reaction of a tetracarboxylic acid dianhydride with a di-isocyanate to form a prepolymer which is then reacted with a difunctional compound having reactive hydrogen atoms. The resulting copolymer can be formed into high strength fiber or films.
Japanese 7229799 teaches a thermosetting resin containing an imide bond. The resin is produced by heating a linear polyurethane resin, obtained by reacting a polyisocyanate and a polyhidric alcohol with a polycarboxylic acid, its anhydride, mono-or di-alkyl esters or mixtures thereof, in an organic solvent. In an example diphenyl methane di-isocyanate and ethylene glycol and glycerine were reacted in a solvent to produce a polyurethane resin which was then reacted with trimellitic anhydride.
Japanese 4047278 teaches a colorless elastomer of copolyurethanes having amide or imide bonds. Diols of 400-6000 molecular weight are reacted with equimolar quantities of di-isocyanate to form a prepolymer which is then extended using compounds of the formula (HO.sub.2 C).sub.2 --R--(CO.sub.2 R.sub.1-2) or (HO.sub.2 C).sub.2 --R --CO.sub.2 R.sub.1) where R, and R.sub.2 are each equal to H, CH.sub.3 C.sub.2 H5 or phenyl; and R is aliphatic if the di-isocyanate is aromatic or aromatic if the di-isocyanate is aliphatic, and imidizing the product. Preferred deals are polyethylene or polypropyleneglycol or polyesters.
German DT 2017511 teaches polyurethane elastomers with polyimide or polyamide acid structure for highly elastic filaments or films. Linear polyester can be reacted with excess di-isocyanate to form a prepolymer which is then reacted with a molar excess of aromatic or araliphatic diamine which is then polycondensed with a polyanhydride. The resulting polyamide acid is then cyclized at 50.degree. to 300.degree. C.